The present invention relates to the art of optical integrated circuits and more particularly to apparatus and methods for aligning and attaching optical fibers to optical integrated circuits such as planar lightwave circuits.
Optical integrated circuits (OICs) include devices such as 1xc3x97N optical splitters, optical switches, wavelength division multiplexers (WDMs), and the like. Such OICs are employed in constructing optical networks in which light signals are transmitted between optical devices for carrying data and other information. For instance, traditional signal exchanges within telecommunications networks and data communications networks using transmission of electrical signals via electrically conductive lines are being replaced with optical fibers and circuits through which optical (e.g., light) signals are transmitted. Such optical circuits include planar lightwave circuits (PLCs) having optical waveguides on flat substrates, which can be used for routing optical signals from one of a number of input optical fibers to any one of a number of output optical fibers. Optical circuits allow branching, coupling, switching, separating, multiplexing and demultiplexing optical signals without having to transform the optical signals into electrical signals first. PLCs make it possible to achieve higher densities, greater production volume and more diverse functions than are available with fiber components.
The input and output optical fibers are typically formed in a group or array of many such fibers (e.g., 48), where the fiber array is connected to a planar substrate (e.g., an integrated circuit chip) to transmit or receive light to or from waveguides in the OIC. Light from the optical fibers is then provided to optical circuitry within the OIC via the waveguides, wherein the optical circuitry may include switches, multiplexers, or other optical circuitry. The waveguides comprise optical paths deposited on the chip, which are made from glass or other transmissive media such as optical polymers, wherein the waveguides have a higher index of refraction than the chip substrate in order to guide light to or from the optical fibers in the array. The waveguide ends are commonly formed on a sidewall or edge of the optical circuit, whereat the optical fiber ends may be connected with the waveguides. The connection of optical fibers to the optical integrated circuit is sometimes referred to as xe2x80x9cpigtailingxe2x80x9d, where an optical fiber array attached to the optical circuit appears as a pigtail.
In the pigtailing process, the ends of the optical fibers in the array must be aligned with the ends of the waveguides in the OIC, in order to ensure proper transmission of light therebetween. The alignment of the fiber array with a row of waveguides in an OIC involves relative translation of the array with respect to the OIC in six alignment axes. For example, the relative alignment is typically controlled using six axis positioning equipment and associated controls, which control linear positioning in X, Y, and Z axes, as well as rotational alignment in yaw, pitch, and roll axes. As the sizes of the waveguides and the active portions (e.g., cores) of the optical fibers continue to decrease, the alignment in the pigtailing process becomes more critical. However, such multi-axis positioning and control devices are costly, and may be difficult to operate or automate in a production environment.
Conventional techniques for such alignment and attachment include one at a time alignment and attachment of individual optical fibers, which is time consuming and not ideally suited for higher volume production of pigtailed devices. Moreover, the optical fiber array is connected to the OIC via a butt joint, which can be mechanically unstable. Some passive alignment techniques employ V-grooves etched in the substrate, in which the optical fibers may be placed for lateral alignment with the waveguides. However, inaccuracies in the lithographic and etching processes limit the applications of alignment by this methodology.
Active alignment techniques include monitoring the optical transmission of light through the waveguide/fiber interface visually while moving the optical fibers relative to the planar waveguides. In addition to visual monitoring, the transmission monitoring can be performed using a light source providing light to one or more fiber ends, and a light detector. Active alignment procedures typically produce lower loss interconnections, but result in a higher cost per interconnection than passive alignment techniques. Thus, there is a need for passive alignment and attachment techniques and apparatus, which provide the required accuracy needed for ever shrinking waveguide and optical fibers, without having to monitor the transmission during pigtailing, and without requiring complex and/or costly six axis positioning systems.
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Rather, the sole purpose of this summary is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented hereinafter. The present invention provides optical integrated circuits (OICs) having a shelf upon which optical fibers are located, and which provides for passive vertical alignment of fiber arrays with OIC waveguides. A cover plate with channels therein is further provided by which passive alignment in five or six alignment axes can be achieved. The invention thus provides for accurate active alignment without the need for multi-axis positioning and control systems, as well as for accurate six axis passive alignment, thereby facilitating accurate and low cost pigtailing of OICs which may be easily automated for manufacturing.
One aspect of the present invention provides an optical integrated circuit (e.g., such as a PLC) with a base and one or more waveguides extending longitudinally through at least a portion of the base and having waveguide ends facing outward from a generally vertical wall in the base. A shelf is provided with a generally planar top surface extending longitudinally from the wall toward the front end of the circuit. The shelf top surface is located vertically below the waveguides by a vertical distance in order to passively align optical fibers located on the shelf with the waveguides in the vertical direction. A cover plate can then be used to hold the optical fibers on the shelf. The cover plate can have a bottom side either operable to engage the top surface of the shelf, or operable to securely trap the optical fibers between the shelf and the cover plate. The cover plate downwardly facing channels, such as V-grooves, engages the optical fibers between the channel and the top surface of the shelf, and laterally aligns the fibers with the corresponding waveguides. The shelf and cover plate cooperate to form a mechanically stable lap joint between the fiber array and the OIC.
The shelf and cover plate thus allow for five axis passive alignment, for example, with respect to Y, Z, yaw, pitch, and roll. Thereafter, the cover plate and fiber array can be translated laterally to obtain alignment along the sixth (e.g., lateral or X) axis, for example, using transmission monitoring. In addition, a vertical portion can be provided on the cover plate, such as extending vertically downward from the cover plate, which engages with a vertical abutment surface on the OIC, whereby passive alignment in the X axis can also be achieved. Thus, the invention provides for passive six axis alignment without the need for transmission monitoring, and without costly and complex six axis positioning and control equipment.
Another aspect of the invention provides pigtail attachment apparatus for an optical integrated circuit having waveguide ends in a generally vertical wall. The attachment apparatus comprises a shelf with a generally planar top surface extending longitudinally from the wall and vertically below the waveguides. The apparatus also comprises a cover plate having a bottom side with one or more downwardly facing channels to engage optical array fibers between the channel and the top surface of the shelf, for alignment thereof with the waveguides.
Yet another aspect of the invention relates to methods for attaching an optical fiber array to an optical integrated circuit having at least one waveguide with an end facing longitudinally outwardly from a generally vertical wall. The method comprises providing a shelf in a base of the optical integrated circuit, located vertically below the waveguide, and providing a cover plate having a bottom side with at least one downwardly facing channel. The method further comprises engaging an optical fiber between the downwardly facing channel and the top surface of the shelf, and securing the cover plate to the base using an adhesive or other securing techniques.
Still another aspect of the invention provides methodologies for manufacturing an optical integrated circuit, comprising fabricating a base extending longitudinally between front and rear ends, laterally between first and second sides, and vertically between a top and a bottom, and providing at least one waveguide in the base extending longitudinally through at least a portion of the base and having an end facing outward from a generally vertical wall in the base, and providing a shelf in the base with a generally planar top surface extending longitudinally from the wall toward the front end, wherein the top surface of the shelf is located vertically below the waveguide.